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SAN JOSE — A summer afternoon at a neighborhood swimming pool took a frightening turn Thursday when at least 35 people, including kids, were exposed to a dangerous mixture of chemicals after a pool maintenance worker mixed the wrong products.

All of the people exposed to the combination of muriatic acid and chlorine — pool chemicals that created a gas cloud at Shadow Brook Swim Club in Almaden Valley — were decontaminated and transported to hospitals, according to the San Jose Fire Department.

Officials said the victims were taken to nine different local hospitals in 10 ambulances. The patients included children as young as 6 and a number of parents. San Jose Fire Capt. Mitch Matlow said a few of the those exposed to the gas cloud experienced shortness of breath and vomiting, but he could not say whether anyone was seriously injured.

Kaiser Permanente San Jose Medical Center treated six patients for upper respiratory conditions and breathing difficulties, according to a hospital spokesman. Five of those six patients were released from the hospital by 4 p.m. Good Samaritan Hospital reported the three patients taken there for treatment were in “good condition.”

A spokeswoman at Santa Clara Valley Medical Center said the hospital treated four people, but she did not have their names and thus could not provide information about their condition late Thursday afternoon.

At least 35 people, including kids, were exposed to a dangerous mixture of chemicals on June 14, 2018, at the Shadow Brook Swim Club in Almaden Valley in San Jose. (Dai Sugano/Bay Area News Group)

The incident happened just after noon at the neighborhood swim club, which is off Almaden Expressway about four miles south of Blossom Hill Road. The fire department, which sent its hazardous materials team, said the mix of chemicals could be “potentially fatal.”

“We are taking this very seriously,” Matlow said at the scene. “That combination of chemicals can release a gas cloud that can cause what’s called secondary drowning. The lungs start swelling up with its own fluid, the fluid blocks the airwaves and you drown in your own fluids.”

Lindsay Tarasco, 17, was teaching a group of 7- and 8 year-olds when she noticed a few moms urging everyone out of the pool and then an odd smell in the air.

“I smelled something, so I took a deep breath in. Bad mistake,” she said. “I realized there was definitely something poisonous in the air.”

After getting her swim students out of the pool, the group ran away from the smell, Tarasco said, describing a scene she called “a lot of chaos.”

“The kids were definitely freaked out,” she said. “A couple of them were sick, everyone was coughing, couldn’t breathe.”

Matlow said a contractor working for the pool maintenance company hired by the swim club was pouring pool chemicals into containers in the pump room and put at least one of the chemicals into the wrong spot.

Officials said that inside the pool’s pump room, the chlorine level was at 15 parts per million Thursday afternoon — far above the maximum allowable exposure limit below 1 part per million. The swim club was directed to hire an environmental services company with proper equipment to clean up the scene, a process that Matlow said various agencies, including the fire department and the county health department, would oversee.

Matlow said exposure to a high level mixture of muriatic acid and chlorine could potentially lead to serious health consequences. “Long term, those patients could end up on ventilators and be attached to a breathing machine for quite some time until their lungs heal enough to breathe on their own,” he said.

At least 35 people, including kids, were exposed to a dangerous mixture of chemicals on June 14, 2018, at the Shadow Brook Swim Club in Almaden Valley in San Jose. (Dai Sugano/Bay Area News Group)

Matthew Dworkin, 17, a swim instructor and member of the swim team who was teaching a lesson at the pool when the chemical mixture first started to affect pool-goers, was transported to Kaiser Permanente in San Jose, where he stayed for more than an hour. He said after being released that it still hurt for him to breathe and that when he took big breaths, he felt nauseated. His two brothers were also transported to local hospitals and treated, but they seemed to be OK, said their mother, Patty Dworkin, 47.

Rip Nahal, 40, was taken to San Jose Regional Medical Center along with her three children, ages 5, 8, and 10. It was their first week of swim lessons at Shadow Brook.

Nahal was feeling better after going to the hospital, but while it was happening, she said she felt a “tightness of the throat” and a “burning nose.” Her children also are doing better, but their throats hurt when they tried to breathe deeply, she said.

Staci Tenczar, vice president of the Shadow Brook homeowners association board of directors and involved with the swim team, said, “we have no comment at this time.”

According to a 2017 report by the U.S. Centers for Disease Control and Prevention, there were an estimated 4,876 visits to emergency departments in 2012 that occurred after “pool chemical-associated health events.”

A review of 2008-15 California pesticide exposure records identified eight additional instances of toxic chlorine gas releases at public water venues caused by equipment failure or human error that sickened a total of 156 people.

In 2015, an incident in Antioch at the city-run Prewett Community Park affected 34 children who were playing in one of the facility’s five pools. The children, some of whom were taken to local hospitals, began to complain of trouble breathing, stinging eyes, irritated throats and burning skin.

In that instance, the pool’s water pump had apparently stopped running the night before the incident but the chemicals — sodium hypochlorite and muriatic acid — continued flowing into the pipes, where they built up in the small amount of water that remained there. When the pump began working again the following afternoon, the now-concentrated mix was flushed into the pool, according to county officials.

Annie Sciacca joined the Bay Area News Group in 2016 and covers Contra Costa County. She has written for Bay Area newspapers and magazines on topics including business, politics, economics, education, crime and public safety. Have a tip? Reach Annie at 925-943-8073 or by email at asciacca@bayareanewsgroup.com. You can also send her an encrypted text on Signal at 925-482-7958.

John Woolfolk is a reporter for the Bay Area News Group, based at The Mercury News. A native of New Orleans, he grew up near San Jose. He is a graduate of the UC Berkeley School of Journalism and has been a journalist since 1990, covering cities, counties, law enforcement, courts and other general news. He also has worked as an editor since 2013.

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